Method of fabricating complex microcircuit boards, substrates and microcircuits and the substrates and microcircuits

ABSTRACT

A substrate and method of manufacture wherein a substrate is molded from particulate material wherein grooves on and through the body are formed during substrate molding and prior to sintering. The substrate includes all buss structure molded therein. Cooling of chips is provided by providing a heat sink in grooves formed within a substrate and beneath the chips. Microcircuits are formed by disposing on the substrate and interconnecting via buss structures on the substrate various semiconductor dies with encapsulation of some or all of the substrates and components thereon, if desired. In addition, connection from the board to external circuits is available by means of an edge connector.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of application Ser. No. 445,017,filed Nov. 29, 1982, abandoned, which is a continuation-in-part of myprior application Ser. No. 174,929, filed Aug. 4, 1980, now U.S. Pat.No. 4,374,457.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the fabrication of complex microcircuit boardsand substrates, complex semiconductor circuits using the microcircuitboards and substrates and methods of producing same.

2. Description of the Prior Art

The art of forming shaped articles from particulate mixtures is wellknown. Classically a desired particulate material is mixed with a binderand then formed into the desired shape, this being called a green body.The green body is then fired to provide a fusion of the particulatematerial and drive off the binder, thereby producing the desired shapeproduct with proper surface texture, strength, etc.

In the production of micro-electronic substrates in the manner abovedescribed, it has been a practice to mix the particulate material,usually ceramic, and a thermoplastic binder system together and cast themixed system onto a moving belt. The cast mixture is then adjusted to agiven thickness by the use of a scraper or doctor blade. The greenceramic material, thus doctor bladed to a given desired thickness, isusually permitted to evaporate out a portion of the thermoplastic binderand the green dried sheet is then cut into desired lengths for furtherprocessing.

The green ceramic sheets thus formed have had a considerable amount ofeffort and cost expended in maintaining them to a specific thickness andevery effort is also expended to maintain the sheets throughout theirprocessing in a configuration in which the surfaces are as flat andparallel as possible. In subsequent manufacturing steps, alterations aremade to this thin, flat, parallel-faced geometry by such techniques aspunching holes through the green ceramic, laser scribing the greenceramic to cause depressions in the green ceramic, the passage of thegreen ceramic beneath a saw or grinding wheel to scribe or machine aconfiguration into its surface and other techniques that are very welland thoroughly described in the literature of this art.

Subsequently, additional coatings are applied to the ceramic by one ofseveral well known techniques, such as silk screen printing on to theflat surfaces of the ceramic substrate. In any case, the acceptedpractice starts with a ceramic substrate which is manufactured in acontrolled flat configuration and is subsequently worked by a machiningor other mechanical manufacturing process to alter the surfaceconfiguration to something other than a flat surface. As the greenceramic is quite delicate, the degree to which the flat, as formed,surface can be mechanically altered into a complex three dimensionalconfiguration is severly limited and the ability to closely control thegeometry of the holes is also severely limited.

In a complex hybrid substrate in which a great many components, bothactive and passive, are located on the substrate and interconnected toeach other and to the outside world, the interconnection problem isextremely severe. Many components that are affixed to the substrate,such as micro-electronic circuits and transistors, are interconnectedwith the conductive paths formed on the substrate by means of fine wireswhich are welded to sensitive areas, termed pads, on the transistors ormicro-electronic circuits and terminated on the substrate by anotherweldment to a conductive area on the surface of the substrate. The wiresthat are utilized for these complex interconnections are extremely fineon the order of magnitude of 0.0254 millimeters in diameter. Frequentlydue to the interconnection requirements of the particular hybridcircuit, the wire must pass over another conductive path usually,though, not necessarily limited to a metallized region on the substrate.When this is necessary, what is usually done is to provide, throughmultiple silk screening and firing techniques, an insulating layer thatseparates the two conducting paths so that a short circuit will notoccur at the region of cross over.

Another problem prevalent in conventional substrate manufacture is thatwhen the prepared substrate is fired, the shrinkage due to sintering isnot uniform and not totally predictable When the non-uniformity of theshrinkage of the substrate exceeds the tolerance limits of thesubsequent silk screen printing operations on the surface of thesubstrate, it becomes impossible to register the printing on thesubstrate with any through holes that may exist on the substrate. Thiseffect places a limitation on the size of the circuit being fabricatedas any arbitrarily small size must be within the limits of these twoindependent manufacturing steps.

Another limitation found in conventional high density microcircuitboards and substrates is the dissipation of the heat generated in thehigh density packaged components in that the heat generated by placingcomponents closer and closer together becomes progressively moredifficult to dissipate and get away from the surface as the circuitdensity increases. The conventional solution to this problem is toemploy a substrate material that has the highest possible thermalconductivity. This is generally beryllium oxide which is generallyconsidered to be highly toxic.

A yet further problem inherent in prior art multiple layer ceramicsubstrates is the fact that the green substrate surfaces are not flatafter the thick film material has been applied to that surface becausethe thick film material provides a ridge above the surface and, for thatreason, when the "green" substrates are layered, one atop the other withconductive patterns therebetween and pressure is applied to themultilayer "green" substrate, excessive stresses are set up that resultin low fired yields of the sintered multilayer substrate.

A still further problem is that, in thick film devices, as the conductordimensions become progressively smaller, the cross-section geometry ofthe applied conductor layer becomes less predictable as it is applied asa silk screen ink in thick film technology. Thus, the distributedcircuit constants such as inductance and capacitance have a wide rangeof unpredictable values from substrate to substrate and, in circuitsthat are critical to these parameters, they must be individually trimmedafter manufacture If the thin conductor is buried in a multiple layerconfiguration, the post sintering trimming becomes impossible.

BRIEF DESCRIPTION OF THE INVENTION

The size reduction, packing density, heat dissipation, conductorgeometry and complex interconnection problems are substantially reducedor overcome in accordance with the present invention. Briefly, the greenbody from which the substrate is fabricated is formed by mixing togetherinto a homogeneous mass ceramic particulate material and a thermoplasticbinder. The ceramic-binder mixture is caused to flow into a mold or diecavity under heat and pressure. The die cavity can contain all of thedesired configuration including three dimensional configuration of thesurfaces, the geometry of all surfaces, all through holes, conductorgeometry and any side holes. The molded substrate may then be introducedinto another mold cavity and have subsequent shots of material, notnecessarily of the same composition, which can be electricallyconductive, insulative or whatever is appropriate mated to it in thegreen state. It may be desirable to mechanically work the molded greensubstrate between molding operations by adding or subtracting materialtherefrom. After the desired green molded configuration has been builtup, including multilayer laminated configurations, the molded substratethen has the thermoplastic binder material removed and is sintered toits final dense configuration in accordance with prior techniques as setforth, for example, in Strivens U.S. Pat. No. 2,939,199, Wiech U.S. Pat.No. 4,197,118 or Wiech U.S. Pat. No. 4,305,756.

After sintering, it may be desirable to apply electrically conductivematerial to the bottom of certain grooves molded into the substrateand/or fill other grooves that have been molded into the substrate orover or above the grooves with electrically conductive or otherappropriate material, or run conductive material above the tops ofgrooves with or without interconnection from groove to groove. Ingeneral, those grooves, which have electrically conductive materialapplied only to the bottoms of the grooves will be part of bussstructures and will have highly configured grooves that have been formedto accept various standard bonding tools. Other grooves that areintended primarily to be used as conductive paths will be much smallerand shallower, though a considerable third dimension will be apparent inthese grooves. These conductor grooves are placed on the uppermost planeof the substrate or the lowermost plane of the substrate or both. Thebuss structure grooves will consist of a series of parallel grooves withessentially a corrugated-like appearance. A wire bonded to theconductive material in the bottom of one of these buss structurecorrugated grooves that is brought across the buss structure to atermination point cannot short circuit to the conductive material at thebottom of adjacent or other grooves over which the conductor passes dueto the geometry that has been molded into the surface. The result isthat it is not necessary for the provision of special non-conductingareas to separate conductors that are crossing each other in thisconfiguration. The conductors that have been placed in the groove in theuppermost surface of the substrate can be fabricated as fine astechnology permits and, since they are an integral portion of thesurface configuration of the substrate, they will always run between twoarbitrary points on the substrate, irrespective of the possiblenon-uniformity in shrinkage, as they are molded as a portion of thesubstrate and not subsequently printed onto the substrate. Theseconductors will substantially fill the entire groove up to the substratesurface.

Raised conductors are fabricated by molding raised structures andmetallizing the uppermost portions of these structures. Raisedstructures can be terminated in geometrical configurations that matchthe pad areas on semiconductor chips so that the chips can be bondeddirectly to the substrate by the practices employed in "flip-chip"bonding techniques. Such raised conductors can be disposed on thesubstrate surface and/or in depressions in the substrate.

Holes with axes that are molded substantially parallel to the surface ofthe substrate can be employed as coolant passages so that active orpassive cooling can be readily accomplished, thereby minimizing the heatdissipation problem.

In addition, semiconductor chips can be sandwiched between sinteredsubstrates with conducting paths on facing sides of an adjacent pair ofsubstrates contacting conductive pads on one or more semiconductor chipsmounted between the substrates.

In the event semiconductor chips are already on a substrate, theadjacent substrates are joined by an epoxy or other appropriate joiningagent for ceramics. In the event the substrate does not containmaterials adversely affected at the ceramic sintering temperature,plural substrates can be mounted in intimate contact with each other toprovide joining of adjacent substrates by sintering of the ceramicmaterial between adjacent substrates. Cooling or heat removal caused byheat producing components can take place by means of a heat sinkmaterial disposed in holes in the substrates adjacent the chips. Forexample, the holes could be internally configured as a heat pipe andfreon could be passed through the holes in a closed heat pipe circuitwithin the substrate to conduct the generated heat to a heat sinkregion. In this way, heat can be removed from above and/or below and/oralong the sides of chips and conductive paths can also contact pads onsingle chips simultaneously from two different substrates. Bumps, asnoted above, can also be placed on one or more substrates. A coolingmedium can also be passed between adjacent substrates, the medium merelyrequiring the properties of being a heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a preferred embodiment of the present invention;

FIG. 2 is a view taken along the line 2--2 of FIG. 1; and

FIG. 3 is a view as in FIG. 1 but prior to firing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be understood that while the discussion of thespecific embodiments of the invention will be provided mainly withreference to ceramics, parts of the invention also apply to metals,plastics, and any other materials that can be made to be moldable. Inthe manufacture of complex microcircuit boards and substrates, it hasbeen necessary in the prior art that these parts undergo precisionmachining and/or printing operations in order to provide the finalarticle with the desired characteristics. In accordance with the priorart, the formability limitations and the requirement for independenttolerancing limited yields and complexity of the desired final articles.In accordance with one aspect of the present invention, ceramicmaterials can now be molded directly from particulate material toprovide the precision finished product without the necessity ofmachining and substantially reducing other costly processing steps.

FIGS. 1 and 2 present a preferred embodiment of the invention. Withreference to FIGS. 1 and 2 there is shown a portion of a substrate 1,preferably of aluminum oxide. Element 2 is a semiconductormicro-electronic device, commonly referred to as a die or chip, whichhas been attached to substrate 1 in well 30 formed in the substrate withchip attachment material 7 which is known in the art. The chip is inelectrical contact with conductive material 22 located in the via 8which forms a power connection to the chip. The chip is located adjacentto through hole 9 which is a molded internal cooling passage of adesired geometry, not necessarily circular, and passes entirely throughthe substrate though it need have only one outlet. Through holes 15 and16 pass entirely through the substrate from top to bottom surfaces andhave been filled with conductive material 23 to offer electricallyconductive paths from one surface of the substrate to the other.Conductor 17 has been silk screened onto the substrate and connects theconductive material of hole 16 to that of hole 15. Conductor 17 couldalso be disposed in a groove formed in the substrate during molding. Padarea 6 has been molded into the top side of the substrate and has beenfilled with conductive material 23. The buss structure shown consists ofgrooves 10, 11, 12, 13 and 14. These grooves have been dimensioned andcontoured to accept a bonding tool that welds wire 3 to the conductivematerial 24 at the bottom of groove 14 at the weldment shown at location14a. The other end of wire 3 is shown welded to chip 2 at location 3a.Wire 4 is shown welded to chip 2 at location 4a and to pad 6 at location5. It is seen that wire 3 crosses the conductive material in the bottomof grooves 10, 11, 12 and 13 and is supported and maintained away fromthe conductive pads by the material separating the grooves. Thus, theneed for applying an insulating layer covering the conductive material24 is obviated and connections to the grooves of the busses may be runacross the buss structure without possibility of short circuit.Alternatively, bonding pads can be placed at predetermined locationsbetween the grooves 10 through 14 for bonding of the wire 3 thereto foradditional mechanical rigidity. The buss structure groove material 24 atits highest point of elevation, is located a small distance ΔH below thetopmost plance of the structure. Grooves 18, 19, 20 and 21, on the otherhand have been filled with conductive material to the topmost plane ofthe structure with a connection 25 shown running from hole 15 toconductor 18. Conductive material could, alternatively, be disposed on araised portion or portions in the well 30 and such raised conductiveportions could be disposed about the floor and/or sides of well 30 forconnection to pads on chip 2 in the form of a lead frame. The raisedconfiguration could also be replaced by vias with conductive material inthe floor and/or sides of the well 30.

Referring now to FIG. 1, the top surface of the substrate withsemiconductor chips connected thereon is shown. The. chips 2 are bondedto the substrate along the perimeter of a rectangle with connectionsbeing made from chip pads to busses 10, 11, 12, 13 and/or 14 via wire 3,connection to buss 14 being shown. A lead 4 is also connected from a padon chip 2 to the conductive material 23 in hole 16. A buss 25 isconnected between conductive material 23 in hole 15 and buss 18. Achannel 9 positioned in the substrate just below the chips 2 is shown inphantom. The channel 9 can be provided along the x and/or y axis andthere can be several to remove heat from all chips and other heatproducing elements on the substrate as will be explained.

FIG. 3 shows the green substrate as molded that is shown in its firedand final assembled version in FIG. 2. Note the difference in the scalefactors.

The mold or die required to form the final configuration must be scaledup from the dimensions of the final configuration by approximately 20percent, i.e., the final desired dimensions must be multiplied byapproximately 1.2 to determine the mold dimensions. The exact scalingfactors involved are highly dependent upon the specific formulations andprocessing techniques utilized. The shrinkage in processing andsintering however is quite isotropic, so that all dimensions shrink verynearly to the same scale factor. The isotropic nature of the shrinkageinsures that the angles maintained are very nearly identical in thegreen and fired article. The molding material employed here typicallywould be approximately 60% by volume of a fine grain aluminum oxidewhich has been milled to its ultimate crystal size and 40% by volume ofa thermoplastic binder mixture. A typical formula for the thermoplasticbinder mixture would be approximately one-third by weight ofpolyethylene, one-third by weight of paraffin wax, one-third by weightof beeswax with perhaps 0.1 through 0.2 percent of stearic acid added.The thermoplastic materials and aluminum oxide are mixed and blendedtogether to a homogeneous mass at a temperature in excess of the meltingpoint or flow point of the thermoplastic materials. Techniques forproducing thermoplastic molding mixtures are well described in the priorart and will not be elaborated on here.

The cooled green molding material is crushed to pellet size or otherwisepelletized and is employed as a feed material for a substantiallyconventional plastic injection molding machine that has been suitablymodified to accept abrasive materials.

The mold is constructed preferably of ceramic, though metal and cermetscan also be used, by techniques and principals well known in the art ofplastic injection molding.

The vias 10 through 14 and 18 through 21 in the final mold may be ofsuch small cross section that they cannot be accurately and properlyformed in the mold by standard or known mold-making techniques. Onenovel method of accurately forming such vias in the final mold is toproduce a first mold with all geometry multiplied in size by apredetermined factor so as to permit formulation of the vias by standardor known mold-making techniques. A second mold is then formed from thefirst mold by the techniques described above and in the above notedpatents for forming substrates except than metal rather than ceramic ispreferably used. This second mold will be a negative of the first mold,but reduced in size uniformly throughout by about twenty percent. Athird mold is then made in the same manner as the second mold from thesecond mold which is a negative of the second mold and again reduced insize by about twenty percent. This procedure is continued until asubstrate mold of the desired size results. There is substantiallycomplete replication of the molds from step to step in reduction.

The holes 9 are formed, for example, by having an insert in the mold inthe form of an electrically conductive wire of proper cross section andlocated where the holes are to be formed. When the green body is formed,the molded part with wire is removed from the mold and the wire isheated sufficiently to melt the binder immediately therearound andpermit axial removal of the wire, thereby leaving the hole 9 in thegreen substrate in the region where the wire had been.

Other methods of forming holes include placing an extractable materialin the substrate at the location wherein the hole is to be located. Forexample, a length of nylon 612 can be used by placing it in the mold asan insert and the ceramic material is molded around the nylon, encasingthe nylon totally except for one or more exits to the substrate surface.The ceramic binder is designed to be inert to formic acid whereby thenylon 612 can be later removed from the "green" substrate by dissolvingit in formic acid. The insert could also be a material which burns awayduring sintering without adversely affecting the remainder of thesubstrate. This is essentially a "lost wax" casting process type ofoperation. It should also be noted that the hole 9 can have any shapedesired such as serpentine or the like. The important feature is thatthe hole be located as close as possible to all heat producingcomponents disposed on the substrate.

Subsequent manufacturing steps for specific devices and specificsubstrates may vary widely at this point. However, it is to be clearlyunderstood that, irrespective of the variations in manufacturing stepsand procedures that may take place at this point, at least a singlemolding operation has occurred and that the substrate may be reinsertedinto different cavities and subsequently may have an additional layer orlayers of the same or different materials compatible with the endobjective of the substrate molded on or into or through the substrate.The number of combinations and permutations possible at this point isvery great and anyone skilled in the art will be well aware of thenumber of possibilities that exists to them to manufacture the desiredend item. Enumerating such possibilities would not materially contributeto the description of this invention and for the purposes of thisdescription it will be assumed that no additional steps will be takenbetween the molding and firing of this particular device. However, alist of possible operations that could be emploved during this greenphase, though by no means complete, would include the followingpossibilities: (1) machining, (2) silk screen printing, (3) coating withresist and exposing, (4) filling grooves and vias, (5) laminating, (6)thermal welding, (7) thin film deposition, (8) plating.

Sintering of the substrate is accomplished in two distinct steps. First,the thermoplastic binder must be removed from the substrate. This isconveniently accomplished by slowly heating the substrate at a lowpressure to evaporate or sublime thermoplastic material out of thesubstrate body as described by Strivens, however other methods such asdescribed in the above listed patents are equally appropriate. Second,the substrate is then sintered with a sintering schedule and sinteringatmosphere that is compatible for all the materials included in thesubstrate. If, for example, during substrate fabrication, a molybdenummetal face had been screened onto the green substrate at some portion ofthe manufacturing process, then the sintering atmosphere would best bereducing in nature. However, if the entire substrate is composed of anceramic oxide such as alumina, then the sintering is most convenientlyperformed in an air atmosphere. Beneficial use of sintering atmosphereis well known in the art.

The next step in the manufacture of the subject circuit is to apply themetallization to the desired locations in and on the substrate. Thetechniques employed to do this are well known in the art and theexamples presented here are typical approaches that would be taken toachieve this objective. Grooves or vias 18, 19, 20 and 21 are mostconveniently metallized by spreading or doctor blading an electricallyconductive metal glass frit composite slurry or paste such as is usedfor silk screen printing across the groove area, thereby filling thegrooves.

The metallizing paste is dried and the substrate fired in accordancewith the procedure required for the particular metallizing pasteemployed. As the groove structure under consideration here is located inthe uppermost plane of the substrate, the metallizing paste that isbridging the gaps and spread about on the substrate surface inundesirable locations is most conveniently removed by mechanicallyabrading or lapping the uppermost surface. If the substrate is applieddirectly to the lap, only the uppermost plane comes into contact withthe lap, thereby removing any material on that plane. In this manner theconductor grooves are filled with a metallized material which hasassumed the geometry of the grooves. Through holes 15 and 16 are filledwith the same pass of metallizing paste as was employed in the fillingof grooves 18, 19, 20 and 21. At this time bonding pad 6 is also filledand bonding pad 6 is lapped back during the clean up operation that wasemployed to clean the regions surrounding the grooves 18, 19, 20 and 12.Conductor 17 is applied in this example most typically by silk screeningthe metallizing paste so that a conductive path between the hole ends ofholes 16 and 15 are joined by metallizing material. The bottoms ofgrooves 10, 11, 12, 13, 14 and groove 8 are most conveniently filledwith well known electrically conductive paste utilizing an inking pen ofsmall bore capillary tubing. To insure the separation of conductivematerial between the grooves, it may be desirable to coat the uppersections of the grooves with a non-wetting wax resist which is mostconveniently applied by a roller. While the conductive paste is in itsgreen form, it may be conveniently tested for continuity andinterconductor short circuits and repaired at this time prior to firing.In order to set the conductive material in its place, the substrate isfired at an elevated temperature with a time temperature atmosphereprofile that has been established for optimum firing conditions for thepaste being employed. It is obvious that a multiplicity of pastes andfiring schedules may be employed for specific purposes, such as to applyresistant pads. It is apparent that the conductive paste can be appliedto the "green" substrate and fired in the same step as the sintering ofthe "green" debinderized substrate or it can be applied to the substrateafter it has been fired or sintered, thereby requiring a further firingstep. It is also apparent that other sinterable materials can bepositioned on the "green" substrate, such as resistive, insulative orthe like. For example, materials resulting in piezoelectric devicesafter sintering can be deposited on the substrate or in grooves thereonwith an electric field thereacross being provided by conductors inadjacent grooves. Also, resistors, capacitors and other such componentscan be formed.

An alternate procedure for applying conductive paths at preselectedlocations on the substrate, either before or after firing or sinteringof the substrate is by use of a thermographic slurry in which thecontinuous phase is a thermoplastic material and the particulate phaseis a combination of a glass frit and a conductive powder, in general.The slurry is solid at ambient temperature and a liquid at apredetermined temperature above ambient. With the slurry in the liquidstate, it is applied to an inking type device, such as a rubber stamp,wherein the pattern on the stamp is heated to permit the slurry to bedeposited on the pattern in the liquid state. The pattern takes theshape of the conductive pattern to be deposited on the substrate. Thestamp is then properly lined up with the substrate and the pattern thencomes into contact with the substrate to deposit liquid slurry thereon.The stamp type device is removed from the substrate, leaving the liquidslurry thereon in the pattern configuration. The substrate is maintainedat a temperature below the hardening temperature of the slurry wherebythe slurry hardens on the substrate in the shape of the pattern. Thethermoplastic material is then removed by known debinderizingtechniques, such as described in the abpve noted patents. The remainingglass frit and metal powder is fired either during substrate sinteringif placed on a "green" substrate or as a separate step if placed on analready fired substrate to provide adherence of the glassfrit-electrically conductive metal conductor to the substrate.

The stamp type device can have either a flat pattern thereon or a threedimensional pattern whereby the "ink" thereon can be deposited ingrooves or wells formed in the substrate. For example, the patterndeposited could extend along the side walls and/or bottom of the well 30in FIG. 2.

The stamp type device can be of any material capable of having a patternformed on a face thereof and being wetted by the "ink". Preferably thepattern is heated as noted above. However, the pattern need not beheatable and can still be used as long as the "ink" is maintained in theliquid state up to the time of pattern removal from the substrate. Thiscan be accomplished by heating the slurry or "ink" to a sufficientlyhigh temperature initially.

The slurry or "ink" if designed to be electrically conductive, iscomposed of a glass frit of the type used in silk screen techniques, anelectrically conductive metal powder such as standard silver-palladiumalloy powder, a gold or a copper alloy powder and the thermoplasticbinder, such as polyethylene. The glass frit would have a low meltingpoint (about 300° C.), be compatible with the powder and be capable ofadhering to the substrate at a reasonable firing temperature above about300° C. and below the substrate sintering temperature. About 95% to 50%by volume of metal is used and the rest glass frit to produce thepowder-glass mixture. About 50% to 60% by volume powder-glass mixture isused and the rest thermoplastic binder to form the slurry. A typicalbinder is composed of about 0.2% stearic acid, about 90% paraffin waxand the rest polyethylene, all by volume, though other thermoplasticbinders could be used.

The above noted "stamp-type" process can be used to form other types ofpatterns on or in the substrate. For example, the conductive powder canbe replaced with a cermet, an electrically insulating material such asthe glass itself, electrically resistive material, semiconductivematerial, such as barium titanate, or the like to form any desiredpattern in or on the substrate surface. It is merely desirable that suchmaterial be in powdered form and be adherable to the substrate eitheralone or in combination with the glass frit.

After firing and clean up operations, the chip 2 is attached to thesubstrate by any one of the chip attach techniques that are well knownin the art. Element 7 is shown and represents chip attach material thatis unspecified in this description. Conductor 8 has a low ohmic contactto chip 2 and represents in this description a power supply lead to chip2.

The active micro-electronics located in and on chip 2 are interconnectedto the substrate through wires 3 and 4 at weldments 3a and 4a andweldments 5 and 14a as shown as well as to interconnections by wire,whether deposited onto the substrate 1 or by weldments from the chip toother ones of the conductors 10 through 14 and 18 through 21 (not shown)to provide interconnection between chip 2 and other chips on thesubstrate 1 as well as to circuits external to the substrate 1. As iswell known in the art, welding pad regions located at the surface ofchip 2 are provided for this express purpose. The metallizing materialsemployed at locations 5 and 14a have been selected to be compatible withthe weldment. The result is a miniaturized equivalent of a known printedcircuit board with multiple interconnected semiconductor devicesthereon.

It is seen that wire 3, in going from groove 14 to the pad located at3a, crosses conductors 13, 12, 11 and 10. The dimensions of wire 3 arenormally on the order of 0.0254 millimeters and the dimensions acrossthe grooves 10, 11, 12, 13 and 14 would normally be on the order of0.381 millimeters. The conductor 3 is preferably composed of aluminumwith 1% silicon added though other conductor materials can be employed.Thus, very large unit forces would have to be applied to the wire 3 tocause it to contact the conductive material in one of the grooves acrosswhich the wire is suspended. The unit forces would be the same as if itwere a one centimeter diameter aluminum bar bridging a fifteencentimeter gap.

All or part of the substrate can now be encapsulated. For example, anepoxy resin can be sprayed or otherwise coated over all semiconductorchips 2 to provide hermeticity or any other desired properties to thesubstrate, conductors and/or components on the substrate.

It can be seen that, for example, one or more of the chips 2 can bemicroprocessors and/or other complex circuits whereas still other onesof the chips 2 can be RAMs, ROMs or other types of storage device toprovide a complete very miniaturized system such as a computer, controlsystem or the like in a space much smaller than is presently known.Furthermore, these systems can be arranged as shown in FIG. 1 or,alternatively, with a further set of input, output and power bussesextending to the edge of the substrate 1 for connection to a connectorof known type for plug-in connection to known systems.

Cooling passage 9 is utilized to withdraw thermal energy from the chip 2to a remote location to maintain the chip temperature within desiredlimits. This may be done by circulating a fluid, such as freon or air orthe like through cooling channel 9 of a lower temperature than chip 2 tocreate a temprature differential between chip 2 and the fluid in coolingchannel 9, thereby causing a heat flow from chip 2 to the fluid inchannel 9 in accordance with well known thermodynamic and heat transferprinciples. Use may be made of local boiling such as is found in a heatpipe to achieve very high thermal flux densities in the regionsurrounding the chip. These techniques are well known in the art of heattransfer and thermal energy management and are obvious to anyone skilledin this art once the availability of cooling passage 9 is presented tothem.

While only a single hole 9 is shown passing under a single row of chipsin FIG. 1, it should be understood that the hole 9 or holes 9 can takeother configurations. For example, rather than passing from one end ofthe substrate to the adjacent end as shown in FIG. 1, there can also beholes in a transverse direction to pass under or along the sides chips 2positioned from left to right as shown in FIG. 1. Also, a single holecould be formed which is in the shape of a rectangle and passes underall chips 2 shown in FIG. 1 with closely adjacent entrance and exit forheat sink material disposed at a substrate edge. The latter embodimentwould require molding of the substrate in two parts with half of thehole in each part. The parts would then be held together while in thegreen state in the shape of the final configuration with subsequentbinder removal and sintering.

In the preferred embodiment described above, the substrate material wassintered aluminum oxide. Other preferred embodiments include the use ofa metallic particulate material which has been mixed with a suitableplasticizing binder and molded into the desired complex geometry. Thesintered metallic substrate could then be subsequently machined as inthe case of the aluminum oxide substrate, but with the additionalmachine techniques that require a ductile or conductive material. Forexample, precise configuration could be coined into the surface as anextension of a crush forming operation or complex configurations couldbe electrically discharge machined into the surface. In this embodiment,the substrate would then be coated with a thin layer of insulatingmaterial, such as glass. Another embodiment exists in the use of moldinga highly loaded plastic system, such as a glass filled epoxy, anddirectly utilizing the as molded article for the interconnectionstructure without subsequent binder removal and sintering.

As stated hereinabove, multiple substrate layers can be formed, one atopthe other. For example, two substrates of the type shown in FIG. 1 canbe placed back to back in the "green" state with appropriate throughholes and then sintered. Alternately, the substrate as shown in FIG. 2,but with conductor 17 disposed in a groove so that nothing extendsoutwardly beyond the bottom surface of the substrate, is disposed on afurther similar substrate such as shown in FIG. 2 in a top to bottomrelation while in the green state but with conductors formed thereon ofthe type noted hereinabove. With the two substrates in intimate contact,sintering is performed, whereby the substrates are joined with buriedconductors therebetween. The substrates could also be joined by othermeans, such as an epoxy or the like. The number of substrates stackedone atop the other in this manner can be quite large.

A further manner of forming multiple substrates secured to each other isin the molding itself. A substrate of the type shown in FIG. 3 is firstmolded and, while in the "green" state, appropriate conductiveinsulative or other materials are deposited on one surface and ingrooves and depressions therein by conventional techniques or by afurther molding step. In accordance with the further molding step, thealready molded "green" substrate is placed in a mold and the additionalmaterial or materials are molded thereon at predetermined locations andin predetermined grooves and depressions. Plural different materials canbe simultaneously or serially molded onto the "green" substrate by wellknown techniques. In this way, conductors, insulators, semiconductorsand other devices are formed on the "green" substrate. A third moldingstep would involve placing the "green" substrate with materials thereoninto a mold and molding a further substrate over the materials, therebyburying conductors, etc. between the two substrates. This procedure canbe continued to provide the desired number of layers whereupon theentire module is then fired after binder removal in the manner describedin the above noted patents. A multiple layer ceramic module is therebyproduced. Components can further be formed on the exposed surfaces byone or more of the procedures described hereinabove. Encapsulation asdescribed above can now also be performed.

Though the invention has been described with respect to a specificpreferred embodiment thereof, many variations and modifications willimemdiately become apparent to those skilled in the art. It is thereforethe intention that the appended claims be interpreted as broadly aspossible in view of the prior art to include all such variations andmodifications.

What is claimed is:
 1. A method of forming a predetermined pattern on asubstrate comprising the steps of:(a) providing a three dimensionalsubstrate in green form composed of homogeneously dispersed binder andsinterable powder in a predetermined shape, (b) providing a homogeneouscomposition composed of a thermoplastic material and a sinterablematerial inert with respect to said substrate and adherable to saidsubstrate, (c) providing a pattern of predetermined shape wettable bysaid composition when said composition is in the liquid state, (d)wetting said pattern with said composition, (e) placing the compositionon said pattern on a predetermined location on said substrate, (f)cooling said composition on said substrate to cause said composition toset, (g) removing said thermoplastic material and at least a portion ofsaid binder, and (h) simultaneously sintering said sinterable materialand said sinterable powder to provide a sintered substrate of saidsinterable powder with said sinterable material adhered thereto.
 2. Amethod as set forth in claim 1 wherein said sinterable material iselectrically conductive.
 3. A method as set forth in claim 2 whereinsaid sinterable material is a mixture of a glass frit and anelectrically conductive powder.
 4. A method as set forth in claim 1wherein said sinterable material is electrically insulating.
 5. A methodas set forth in claim 1 wherein said sinterable material is electricallyresistive.
 6. A method as set forth in claim 1 wherein said sinterablematerial is electrically semiconductive.
 7. A method as set forth inclaim 1 wherein said substrate has a three dimensional surfaceconfiguration and said pattern conforms to said three dimensionalconfiguration.
 8. A method as set forth in claim 1 wherein said patternis heated to a temperature above the melting point of said compositionprior to wetting said pattern with said composition.